Phenolic resin preforms and method of manufacturing them

ABSTRACT

Premoulding materials having long-term controllable B-stage characteristic, comprising phenol resins, optionally with reagents, additives and adjuvants, are characterized in that they contain hydraulic binder and/or its components as well as an agent that reduces the alkalinity and optionally the content of free metal ions. For its preparation, 1 part by wt. phenol resin is mixed with less than 4 parts by wt. of a hydraulic binder and/or its components as well as less than 0.2 equivalent parts by weight of the agent. The phenol resin premoulding materials according to the invention thicken quickly to a desired B-stage, are capable of maintaining the attained plateau, and thus allow the manufacture of heat-curable composites of desired rheology and reactivity.

The invention relates to phenol resin pre-moulding materials(intermediates) having a controlled B-stage, which cure under theinfluence of heat and, advantageously, under pressure, and also to aprocess for their preparation.

Pre-moulding materials of phenol resins having a long-term adjustableB-stage characteristic, optionally with reagents, additives andadjuvants, which are characterised in that they contain hydraulicbinders and/or their components as well as an agent for reducingalkalinity and optionally the content of free metal ions, are aparticular object of this invention.

Duroplast pre-moulding materials have long been known. They are mouldingmaterial primers in the B-stage, which are more or less stable mouldingmaterials comprising thickened reactive mixtures of the mouldingmaterial starting components. They generally comprise few volatilecomponents, and can be worked directly to finished parts, for example bypressmolding. They are prepared as compounds of prematrix andreinforcing material. The prematrix (paste) principally comprisesreaction or condensation resin and reagents, for example hardener,catalyst, thickener, optionally in admixture with additives such asfillers, pigments, plasticisers and adjuvants, e.g. internal releaseagents, lubricants, wetting agents. The reinforcing materialconventionally comprises fibrous structures, for example cut glassfibers. The thickening or maturation or rather the attainment of thecorresponding B-stage follows relatively quickly, and is usuallyconducted thermally. The resultant material is pseudo-stable, and itsapplicability is limited. The storage of such products is associatedwith further, but slower continuation of the thickening. Thepre-moulding materials become drier and harder. Longer storage at roomtemperature can lead, for example, to extensive hardening. BMC-amorphouspre-moulding materials, prepeg cloth pre-moulding materials and SMC(sheet moulding compounds)-mats pre-moulding materials serve asexamples.

The B-stage of such pre-moulding materials exhibits a stage, in whichthe prematrix of the pre-moulding material, preferably on the basis of adefined increased molecular weight of its reaction or condensation resincomponent, exhibits a definite limited rheology and, as the case may be,autohesion.

The reaction- or condensation resins are no longer fluid, in this state.They are however soluble and meltable. The prematrix can besubstantially solid. Usually, however, it becomes putty-like to somewhatwax-like, and the pre-moulding material has a kneadable to oil clothconsistency. On hotpressmoulding, such B-stage materials behave in sucha manner that their prematrix flows under the influence of heat andpressure, reimpregnates and transports the reinforcing material, conveyseventual gas components, fills the relevant mould space and then gels onreaching the appropriate temperature and cures to a form-giving part ofthe moulded item. The gelling, at the desired end point of the transportphenomenon of the moulded mass in the implement, is characterised by aformation of local networks which largely change to completecross-linking on curing.

The B-stage thus exhibits a quantity characteristic of the materialstate, whose thickening rate, level and stability are of essentialimportance both for the preparation and workability of the pre-mouldingmaterials and for the quality of the resultant parts. The B-stagedetermines the handability of the pre-moulding material (important incomplex mould tool geometry), affects the density of the relevantlaminate moulding stack (significant for intra- and inter-laminarstrengths) and is also decisive as regards the possibility ofmanufacturing moulding stacks for stock (significant in massproduction). The B-stage is relevant for the storage stability of thepre-moulding materials and important for their flow properties oncompression moulding.

It decisively influences the pressure profile structure over thepre-moulding material mass in the compression moulding process, and hasa substantial influence on the distribution of the reinforcing materialin the moulding.

The reaction behaviour of the pre-moulding materials, which is importantfor curing, and hence also the physical properties of the finishedarticles, are likewise influenced by the B-stage and its quality.

The problems associated with pre-moulding materials are therefore, inparticular the reaction or condensation resin systems for themanufacturing of the composites must have a relatively low viscosity(they must permit good impregnation rheology of the appropriate premix,in order that the predominantly fibrous and more often bundle-shapedreinforcing material can be well impregnated), but they mustnevertheless lead to prematrix systems which thicken quickly and asdesired, the thickened stage that is reached should be largely stable,so that the B-stage exhibits a defined long-term characteristic, and thecuring should take place in a technologically favourable manner.

While the initial thickening and curing of the pre-moulding materials isrelatively controlled and can be conducted in many ways, the preparationof such pre-moulding materials with defined, largely stable B-stateoften succeeds insufficiently or only approximately.

The pre-moulding materials must usually be worked quickly, in practice,or stored at relatively low temperatures.

A satisfactory solution, of the problem of the B-state stability ofpre-moulding materials based on phenol resins, remains largely openuntil now despite various attempts.

For example, US-A-3502610 proposes moulding materials based onphenol-formaldehyde resin, which contain 2-6 wt.% of a hydraulic cement.The cement is here introduced as a regulator of the compound rheology(viscosity reducer) and as an improver of the temperature stability aswell as a source of fire-inhibiting properties.

However, such solutions are insufficient, with respect to the B-statestability. The use of the cement in such systems leads to an increase inthe heat-stability and to a positive influence on the fire-resistance ofthe moulding materials, but a flat long-term plateau of the B-stage isnot attained in this way. An increased cement concentration ratheraccelerates the thickening and reduces the storage time.

DE-A-2550779 again describes synthetic resin and condensation syntheticresin products, based on phenol-formaldehyde,phenol-aminoplast-formaldehyde, aminoplast-formaldehyde,resorcinol-formaldehyde or resorcinol-formaldehyde-urea and theircondensates, which are prepared with 1-20 parts by wt. of a cement perpart by weight of the water present in the products given above or usedin their preparation. The cement should be used in stoichiometricamounts in this context, so that all water present originally in thesystem plus water of reaction are set free on hardening of the cement,and the cement thereby hardens the moulding material. A ceramic clayshould be used as rheology regulator or flow regulator of the relevantpre-moulding materials.

Pre-moulding materials according to this Offenlegungsschrift exhibitimproved mould flow characteristics and favourably-influenced masstransport, but their plateau viscosity is somewhat steep. Thedehydrating effect of cement catalyses the condensation reactions of theresols that are present and the B-stage is depressed. Such primers areworked directly (without maturation). Their duration of storage iscorrespondingly short, only about three weeks. The stabilisation or thesufficient inhibition of the molecular growth of the matrix bindingagents is not achieved in this way, and the compressed bodies thicken,relatively stressed. The technical parameters for use of such compressedbodies change quickly, and they require quick working. Advantages of thecement as additive and reactant are not utilised as fully as possible inthis case.

It has already been proposed (CH-A-0624691), to prepare pre-mouldingmaterials of phenol resin systems in photopolymerisable form. Suchproducts do give moulding materials having somewhat longer B-stagecharacteristic, but they have the disadvantage that they are suitableonly for non-filled, very thin, flat moulded bodies and require storagein the dark.

Similar disadvantages are associated with compounding materials that actas B-stage regulators and hardening catalysts with phenol resols incombination with organic acids released under the influence of light(DE-A-3317570).

Pre-moulding materials having radiation-hardenable binding agents havealready been developed (EP-A-0168065). They do permit the preparation ofcomposite primers having long-term stability, but they do not solve theproblem of providing primers having adjustable B-stage-specific rheologyand require storage in the dark, protected against radiation. They alsohave the disadvantage that they are only suitable for the preparation oflaminar products, up to 10 mm thick.

It is also known to prepare compositions of phenol resins for theproduction of pre-impregnated resin mats comprisingphenol-formaldehyde-resols having hardeners and corresponding fillerswith the admixture of an additive that contains at least 20 wt. %, basedon the total weight of the additive, of an alkali or alkaline earthmetal borate, optionally in combination with alkaline earth metaloxides, and is introduced in an amount of no more than 60 wt. %, basedon the phenol resin solution that is used (EP-A-0176378, EP-A-0220105).

Finally, relevant compositions of phenol resins with an additive thatcontains triethanolamine borate or a mixture of an amine and a boronoxide, are also known (EP-A-0249517).

Among the primers of the moulding materials prepared in the artdescribed above, the composite articles based on unsaturated polyesterresins have similar strengths and are characterised by favourableburning properties and high hot mould stability. The primers howeverexhibit a relatively steep B-stage plateau. Their storage stability isabout two months at room temperature, at which they nevertheless becomeincreasingly drier and harder. Even for these relatively well-developedpre-moulding materials, the long-term B-stage characteristic describedabove is attained only to an unsatisfactory extent. Further, on workingsuch materials, the hardening catalyst can lead to corrosion of therelevant implements.

The object of the present invention is therefore to provide phenol resinpre-moulding materials that have a defined and quickly-attainableB-stage plateau having a flat pattern, that have good hardeningcharacteristics and that overcome the disadvantages described above.

The solution of this problem is achieved by means of phenol resinpre-moulding materials or with a process having the characteristicsgiven in the patent claims.

It has been found that pre-moulding materials comprising phenol resins,optionally with reagents, additives and adjuvants, in combination withhydraulic binders and/or components as well as with an agent forreducing the alkalinity and optionally the content of free metal ions,can thicken quickly to a desired B-stage, maintain the plateau thusreached, and thus allow the preparation of heat-hardenable compositeshaving desired rheology and reactivity.

Phenol resins that are used for the production of such pre-mouldingmaterials according to the teaching of the invention, are fluid,preferably neutral or weakly alkaline products of the primarilyalkaline-catalysed condensation of aldehydes with phenol, cresol,resorcinol, xylenol and the like, that can exhibit modification, e.g.with furan resins or other higher molecular weight systems.Phenol-formaldehyde condensates having a molar ratio of phenol toformaldehyde of at least 1:1, preferably 1:1.2-2.0, are particularlysuitable. These condensation resins provide, in the pre-mouldingmaterials, the object of a thickenable binding agent that actspredominantly for the form-giving primary components in the finishedmoulding materials.

As hydraulic binders, hydraulic cements, cement products, highalumina-containing hydraulic binders and all calcium and magnesiumoxide-containing curing materials are used in an amount of less than 20parts by wt. per 1 part by wt. resin. Preferably, 15-150 parts by wt ofa hydraulic binder or 1-15 parts by wt. of its alkaline earth metaloxide are introduced individually or unmixed, per 100 parts by wt. resincomponents.

The desired hydraulic cements are finely-ground hydraulic binders formortar and concrete, comprising essentially silicon oxide, aluminiumoxide, aluminium hydroxide, calcium oxide, magnesium oxide and ironoxide, in particular in calcium silicate, calcium aluminate and calciumferrite form, that harden when mixed with water (hydration). In thedesired pre-moulding materials, the cement functions as thickener,filler, water-absorber, catalyst, migration agent, flame inhibitor,pigment and reducer of the volatile components.

The high alumina-containing hydraulic cements described above arealumina cements characterised by especially high calcium aluminatecontent. Their alumina content generally lies in the range between 50and 80 wt. %. Examples are Secar 50, Secar 71, Secar 80, from thecompany Lafarge Fondu International, France.

Added components of the hydraulic binder include, e.g. mixtures ofcalcium oxide and/or magnesium oxide with hydraulic additives ormixtures of cement with hydraulic additives. Hydraulic additives have nobinding effect alone, without calcium oxide and/or magnesium oxide, butthey contain components which harden at ambient temperature with, e.g.lime in the presence of water. Hydraulic additives are predominantlysilicic acid- and alumina-containing, finely-ground products fromvolcanic tuff. An example is Trass from the company Rhein-Trass GmbH,Federal Republic of Germany. Individual components of the hydrauliccement are, e.g. magnesium oxide or calcium oxide.

As agents for reducing the alkalinity and optionally the content of freemetal ions, compounds are used that neutralise a high alkalinity of thesystem, remove any excess amount of multivalent metal ions of therelevant system, and can inhibit the fast increase of the molecularweight of the relevant cement. For this purpose it is possible to usee.g. salicylic acid, monosodium phosphate, oxalic acid and the like. Theamount of the agent that is introduced is desirably such that the valueof the ratio of the number of acidity equivalents of the agent in thesystem to the number of moles of water in the system is less than 2.Preferably, the ratio lies between 0.2 and 0.05.

The function of the agent in the prematrix of the pre-moulding materialaccording to the invention depends in particular on the influence of therate of increase of the molecular weight of the relevant condensationresin by controlled salt and adduct formation, in particular by changesin the type and concentration of the system electrolytes as well as byreduced basic catalysis. An especial role is attributed to the pHcontrol.

Surprisingly, it has now been shown that, by means of such an agent, thefurther thickening of the condensation resin in consequence of theconventionally favoured condensation by means of the dehydration agent,in particular cement, the condensation promoter, is apparentlyinhibited. Further, it can be established, surprisingly, that theprematrix system according to the invention exhibits faster curing onheat-compression despite inhibited reactivity during storage. Prematrixsystems or premoulding materials having long-term B-stage characteristicand good hardening capacity are thus obtained.

For the B-stage-specific thickening of the relevant prematrix system,the following factors are particularly important: increase of themolecular weight of the reaction resin by salt- and adduct-formation(complex and chelate-formation) as well as by continuing condensationaccompanied ion-exchanger-analogous sorption effects/with the formationof high molecular entities physical thickening by extending of thereaction resin with solids and partial setting of the hydraulic binder.

The thickening proceeds analogously to the prematrix viscosity andexhibits a structure parameter-related property for the characterisationof the prematrix rheology. This property is determined mathematicallyfrom the lateral spread of a sample according to the invention that issubjected to a displacement procedure under a defined pressure and overa predetermined time. It indicates, by how many percent the prematrixsample under test flows more slowly than a sample having a spread rateof 100 mm/min.

As additives, there can be used, e.g. fillers, plasticisers, dyes,stabilisers, hydrophobic agents, low profile additives and furthermaterials added for the purpose of modifying the properties of thesystem.

As adjuvants, there can be added for example lubricants, release agents,wetting agents, aerating agents as well as other system components thatfacilitate or improve the working of the resultant composite articlesand their precursors. The practical manufacture of the premouldingmaterials according to the invention from the starting materials isconducted by their thorough mixing in a manner such that,advantageously, first the phenol resol resin, the additives andadjuvants and then the reagents are combined, whereupon combination withthe reinforcing material follows.

The addition of the hydraulic binder and/or its components and of thealkalinity-reducing agent can be conducted in the form of separate feedsor by the addition of a single mixture of the two main components. Thismixture can be a pulverulent or, preferably, pasty state (referencepowder or active filler paste or reference paste etc.).

The combination of the prematrix with the reinforcing material can beconducted in conventional manner, for example on an SMC-machine , byintensive mechanical thorough kneading of a sheet-like deposition of cutglass fibers between two prematrix films between two plastics sheets(preparation of P-SMC).

Another means of preparing the premoulding material comprises e.g. thecombination of cut glass fibers with the prematrix under continuousstirring, until the fibers are completely uniformly distributed (BMCproduction). No particular procedures or special materials or measuresare necessary in the obtaining of the prematrix-reinforcing materialcomposite.

The obtaining of the pre-moulding material-specific B-state of thesepre-products follows by maturation, preferably at room or elevatedtemperature.

The storage of these products can be carried out at room temperature orpreferably at a temperature below +15° C. The mouldability is then morethan 3 months and possibly up to one year.

The processing of these premoulding materials can be conducted inconventional manner, for example by hot-compression moulding and airjack procedures. The technology itself can be realised in conventionalmanner. It can be conducted e.g. under the conditions similar to theUP-SMC procedure. The resultant parts, in particular the fiber compositetypes, are high-strength unmeltable products having high temperatureresistance and favourable burning properties. Such moulding materialsare particularly suitable for use in areas having high flame safetyrequirements and high demands on heat stability, for example inautomobile construction as protection against heat, corrosion and noisein the exhaust region, in public transport as seating components as wellas interior furnishing components, in the building industry as exteriorand interior panelling and the like.

The following Examples illustrate the invention:

EXAMPLE I

Production of a condensation resin

112.28 parts by wt. phenol and 58.2 parts by wt. formaldehyde wereintroduced into a reactor, heated at 58° C. and mixed within 2 hourswith 0.39 parts by wt. NaOH while maintaining the temperature constantat 58° C. The temperature was then increased to 80° C. and maintaineduntil the desired viscosity was reached. The reaction mixture was thencooled to 40° C. and the pH was adjusted to a value of 7.1 to 7.2 by theaddition of acid. The resultant reaction resin is a satisfactorilyflowable phenol resin having a B-duration of about 90 seconds.

Process of a prematrix

100 parts by wt. of the condensation resin were thoroughly mixed at roomtemperature in a mixing vessel with 4 parts by wt. water, 96 parts bywt. calcium carbonate and 2 parts by wt. zinc stearate. 24 parts by wt.of a white cement and then 4.8 parts by wt. salicylic acid were thenadded to this mixture with continuous stirring and with maintenance ofthe original temperature. The resultant compound can be used, forexample, both for the preparation of BMC bulk moulding compounds andalso for the production of SMC sheet moulding compounds.

EXAMPLE II

Manufacturing of a prematrix of condensation resin, additives andadjuvants and a powder or paste based on hydraulic cement

100 parts by wt. of the phenol resol resin from Example I werethoroughly mixed together with 96 parts by wt. CaCO₃ and 1.8 parts bywt. zinc stearate in a mixing vessel at room temperature. This mixturewas then thoroughly homogenised, with intensive stirring and maintenanceof the room temperature, with 28.8 parts by wt. of a powder comprising amixture of 24 parts by wt. cement and 4.8 parts by wt. salicylic acid,and the system was thoroughly homogenised. Aluminium hydroxide can alsobe used as filler.

Instead of the powder a paste can of course be used in analogous manner,comprising the appropriate amount of cement and salicylic acid, madeinto a paste with, for example, low viscosity polyester resin. Theresultant prematrix and its consequent press material has improvedquality and, in the given case, on account of the carrier used, modifiedproperties.

EXAMPLE III

Processing of a prematrix of condensation resin, conventional additive,magnesium oxide (component of a hydraulic cement) and analkalinity-reducing agent

100 parts by wt. of a condensation resin, prepared as in Example I, wasthoroughly mixed at room temperature in a homogeniser with 3 parts bywt. water, 60 parts by wt. calcium r carbonate, 67.5 parts by wt.Al(OH)3 and 2.0 parts by wt. zinc stearate. While maintaining theoriginal temperature, 3.9 parts by wt. magnesium oxide (in a pasty formwith a carrier comprising low-molecular weight specific polyester) and2.5 parts by wt. calcium dihydrogen phosphate were then mixed with thismixture. The resultant mixture can thicken quickly and exhibits in theB-state a prematrix having long-term storage properties.

EXAMPLE IV

Preparation of a premoulding material in amorphous form (BMC)

The prematrix of Example I was introduced continuously in an amount of100 parts by wt. at room temperature, and with thorough distribution,into 18 parts by wt. cut glass fibers Vetrotex P-276 (the companyGewetex, Herzogenrath, Federal Republic of Germany), 0.5-5.0 cm long.The fibers have a nominal cross-section of 14 μm and are provided withan aminosilane finish. The resultant moulding material is an amorphouspremoulding material having good moulding properties.

EXAMPLE V

Preparation of sheet moulding compounds with non-oriented fibers (SMC-R)

In this Example, the prematrix (PMX) from Example II was worked with areinforcing material on a conventional SMC machine. The reinforcingmaterial comprised cut Vetrotex textile glass roving P 276. The fiberlength was about 2.5 cm. The viscosity of the Prematrix was about 55,000mPa.s. The formation of the P-SMC band was carried out between twopolyethylene films. The SMC-unit was so arranged that the speed was 2.3m/min, the glass charge 900 g/m² and the doctor gap 0.909 mm. Theresultant P-SMC web had a uniform construction, good wetting of thereinforcing material and the following composition:

Glass content=32%, resin content=29%,

Filler content=39.0%

The formation of the B-stage at room temperature takes about 4 days. Thethickened material exhibits the following data, obtained with thePlastometer (SMC-Technologie Derek & Kueper OHG, Aachen):

    ______________________________________                                        Homogeneity coefficient                                                                             HK59                                                    Plasticity coefficient                                                                              PE 9                                                    Characteristic speed  VC 24 μ/sec                                          ______________________________________                                    

The operability and the rheological characteristics correspondapproximately to the situation for conventional SMC products based onunsaturated polyester resins (UP). The storage stability at atemperature below +15° C. was about 1 year, and the working procedurecan be conducted in similar manner to that for UP-SMC materials.Conventionally, the following process parameters apply:

    T.sub.implement =145° C., P.sub.mass =60 bar,

    T.sub.hardening =1 min/mm.

The implement geometry, average size of the press product andstructure-viscosity of the material should also be considered as forUP-SMC. The pressmoulded P-SMC material (finished part) has thefollowing properties:

    ______________________________________                                        Flexural strength   190 N/mm.sup.2                                            Tensile strength     60 N/mm.sup.2                                            Bending E-modulus 14,500 N/mm.sup.2                                           Drop in tensile   10%                                                         strength at RT→140° C.                                          Barcol hardness   69                                                          Fire class        B1 (M1)                                                     ______________________________________                                    

I claim:
 1. A premoulding resin composition having an extendedcontrollable B-stage characteristic comprising a phenol resin, a binderselected from the group consisting of a hydraulic binder, a hydrauliccement, a high-alumina hydraulic binder, calcium oxide and/or magnesiumoxide mixtures with hydraulic additives, and cement mixtures withhydraulic additives and an effective amount of an agent for reducing thealkalinity to produce a premoulding resin composition having acontrollable B-stage extending for a period of at least three months atroom temperature.
 2. The premoulding material according to claim 1,wherein the ratio of the number of the acidity equivalents of the saidagent in the system to the number of the moles of water in the system isless than 2, and wherein the ratio of the number of alkalinityequivalents of the binder in the system to the number of moles ofphenolic OH groups in the system is less than 0.01.
 3. The premouldingmaterial according to claim 1, wherein the binder is a hydraulic cement.4. The premoulding material according to claim 1, wherein the binder isa high alumina-containing binder.
 5. The premoulding compositionaccording to claim 1, wherein the components of the binder are calciumoxide, magnesium oxide and alumina and silicic acid derivatives.
 6. Thepremoulding according to claim 1, wherein the said agent is an acid oracid salt.
 7. The premoulding composition according to claim 6, whereinthe said agent is selected from the group consisting of oxalic acid,salicyclic acid and mixtures thereof.
 8. The premoulding compositionaccording to claim 6, wherein the said agent is calcium bis(dihydrogenphosphate).
 9. A process for the preparation of a premouldingcomposition having an extended controllable B-stage characteristic,comprising a phenol resin, which comprises mixing about one part by wt.phenol resin with less than about 4 parts by wt. of a binder selectedfrom the group consisting of a hydraulic binder, a hydraulic cement, ahigh-alumina hydraulic binder, calcium oxide and/or magnesium oxidemixtures with hydraulic additives, and cement mixtures with hydraulicadditives and less than about 0.2 parts by wt. equivalent of analkalinity-reducing agent to produce a premoulding resin compositionhaving a controllable B-stage extending for a period of at least threemonths at room temperature.
 10. A process according to claim 9, whereinthe binder is introduced separately from the said agent.
 11. The processaccording to claim 9, wherein the binder is introduced as powder. 12.The process according to claim 9, wherein the binder is introduced inpaste form.
 13. The process according to claim 12, wherein the pastecontains, as carrier, a low-viscosity polyester resin having an acidnumber of b 0, a low viscosity epoxy resin and/or tricresyl phosphate.14. A process according to claim 9, wherein the binder is used togetherwith the said agent in powder or paste mixture form.